Rigid foams having polyisocyanurate structures are known in the art to be highly cross-linked polymers. Due to the thermally-stable structure of the isocyanurate ring, polyisocyanurate foams typically possess high temperature resistance, high dimensional stability to heat and excellent flame-resistance properties. When a polyisocyanurate foam is produced using a physical blowing agent with low vapor-phase thermal conductivity, such as a hydrocarbon, hydrofluorocarbon or similar material, the resulting foam can exhibit excellent insulating properties. These two characteristics, excellent high-temperature stability and good insulation properties, account for the widespread use of polyisocyanurate rigid foams as thermal insulation in residential and commercial buildings. When provided with appropriate metal facings, such foams may also be used as insulated exterior roof and wall panels in the commercial building industry. Processes for the production of polyisocyanurate foam are known and have been described, for example, in DE 1,112,285 and in GB 1,104,394, and typically are carried out by reacting organic polyisocyanates with known trimerization catalysts in the presence of materials, such as foam stabilizers, blowing agents and optionally, polyols. The polyisocyanate typically used in such preparations is crude polymeric diphenylmethane diisocyanate (PMDI).
Because of ever-escalating gasoline prices, higher oil usage and static U.S. domestic oil production, increasing emphasis has been placed upon reducing U.S. reliance on imported oil. One route to decreasing this dependence is to find alternative, sustainable raw materials to produce products that currently are made from petroleum-based resources. Among such raw materials are renewable, biobased products made from natural oils obtained from plants. Recognizing this point, in 2002 the U.S. Congress enacted the Farm Security and Rural Investment Act (“FSRIA”). FSRIA awards preferential treatment to biobased materials in the Federal procurement process to increase the U.S. Government's purchase and use of biobased products as one way of helping to lessen the country's need for oil. FSRIA also establishes a procurement preference program for Federal agencies and their contractors and a labeling program to enable the marketing of biobased products. To utilize the highest possible amounts of biobased materials the U.S. Department of Agriculture (“USDA”) has established guidelines on the minimum biobased content for several generic groupings of materials that require procurement preference for Federal agencies. For example, in the area of foam insulation for wall systems, a minimum biobased content of 8% by weight is proposed. Therefore, a need exists to increase the biobased content of foam systems used in wall systems to meet the Federal procurement guideline.
As mentioned above, polyisocyanurate foams are produced by polymerizing an isocyanate component using a trimerization catalyst, typically in the presence of a polyester polyol or polyol mixture containing both a polyester polyol and polyether polyol. Except for small amounts of sucrose, sorbitol or glycerine which may be used in preparing the polyether polyol, such foams are made primarily from petroleum-based materials. A number of workers in the art have understood this and attempted, even before the enactment of FSRIA, to provide foams that have a reduced content of petroleum-derived materials, with varying degrees of success.
U.S. Pat. No. 5,910,515, issued to Chittolini, discloses a polyurethane or polyisocyanurate foam derived from a mixture containing a crude isocyanate component and a polyol component which contains all or some of the following in a homogeneous mixture: polyols, catalysts, surfactants, water, flame-retardants, fillers, dyes, pigments, expanding agents (i.e., blowing agents) and a compatibilizing agent for the expanding agents. Among the expanding agents disclosed is a pentane component. The compatibilizing agent is said to be a dialkanolamide derived from oily or fatty substances of vegetable origin and present in an amount of at least 5% by weight relative to the weight of the polyol component. The solubility of the pentane in the polyol component is said to be enhanced by the presence of the dialkanolamide.
Hickey, in U.S. Pat. Nos. 5,922,779 and 6,359,022, describes a polyurethane or polyisocyanurate foam formed by the reaction of a polyisocyanate with a polyester polyol-based resin blend containing an aromatic polyester polyol formed by an inter-esterification reaction between a phthalic acid based material, a hydroxylated material and a hydrophobic material. The mixture also includes a nonionic surfactant and a C4-C7 hydrocarbon blowing agent. The hydrophobic material is said by Hickey to be one or more of castor oil, coconut oil, corn oil, cottonseed oil, linseed oil, olive oil, palm oil, palm kernel oil, peanut oil, soybean oil, sunflower oil, tall oil, tallow and mixtures thereof.
U.S. Pat. No. 6,071,977, issued to Austin et al., details a process for producing a polyurethane or polyisocyanurate by reacting a polyol and a polyisocyanate in the presence of an oil component selected from naturally occurring drying and semi-drying vegetable oils, hydrogenated derivatives or methylated derivatives of those oils, and mixtures thereof, with the oil component being a liquid having a boiling point of at least 175° C. and an organosiloxane copolymer surfactant. Among the oil components disclosed are soybean oil, Lincoln bean oil, Manchurian bean oil, corn oil, safflower oil, palm oil, linseed oil, sesame oil, perilla oil, cottonseed oil, coconut oil, dehydrated castor oil and olive oil.
Shieh et al., in U.S. Pat. No. 6,133,329, describe methods of making aromatic polyester polyols that are said to be suitable for use with hydrocarbon and hydrofluorocarbon blowing agents. Those polyols are made by reacting polyethylene terephthalate dissolved in a solution containing a plurality of glycols with a natural oil. The natural oil is said to react into the polyol backbone at a specific temperature. The polyols are said to exhibit low hydroxyl numbers and low viscosities. Hydrocarbon and hydrofluorocarbon blowing agents are said to be soluble in the polyols of Shieh et al.
WO 2004/005365, in the name of Raceina et al., discloses rigid polyisocyanurate foams which are said to have improved thermal stability that are made with an aromatic polyester polyol or polyol blend having an average hydroxyl functionality of less than about 3.0, a polyisocyanate in a sufficient amount to yield an NCO/OH index of at least about 200, a sugar or carbohydrate having a molecular weight of less than about 2,000 and a blowing agent. The foams of Raceina et al. may also contain flame retardants, stabilizers, and other additives.
While the art above does incorporate biobased materials into polyisocyanurate foams, those materials are present in only minor amounts. One explanation may be that polyols based on natural-oils have a chemical structure that is more aliphatic and less polar than typical polyester polyols, which can lower mechanical and burn properties. Thus, petroleum-based polyether and polyester polyols are still used to produce a majority of polyisocyanurate foams. A need continues to exist in the art for rigid, polyisocyanurate foams which have both a high content of biobased materials and performance characteristics similar to existing foams made from petroleum-based raw materials.